Conventional railcar suspension systems are well known in the industry and typically consist of a railcar body with body bolsters and three piece trucks. The car body bolster is located directly beneath the underside of the railcar and a car body bolster typically extends across the entire width of the railcar and has a male center plate bowl for transferring loads. The three-piece trucks are typically comprised of two longitudinally extending sideframes interconnected by a laterally extending truck bolster. The sideframes are generally positioned parallel to both the wheels and rails. The railcar body usually rests upon a truck located at each end of the railcar. The truck is typically connected to the railcar body bolster through a female truck bolster center plate bowl which mates with the corresponding male railcar body bolster center plate bowl.
In conventional freight cars (i.e., box cars, hopper cars, gondolas), the sides of railcars are structurally designed to carry the payload and the load path can be traced through the illustration shown in FIG. 1. For the sake of this discussion, the designation "P" will represent the payload of the railcar as well as the weight of the car and FIG. 1 illustrates that the load P is first distributed to an underlying railcar upper structure at 8, which laterally extends across the width of railcar 5. Upper structure 8 is typically constructed from a heavy structural component such as an I-beam, H-beam, or other channel shape which will statically and dynamically offer resistance to the deflection and bending moments caused by load P. From upper structure 8, the load is transferred into shear plate 12. Shear plate 12 is a structurally heavy plate which coexists with upper structure 8, longitudinally extending underneath the car, thereby providing a stable, extended base for railcar body bolster 20 to receive forces P therefrom. As seen from the illustration, body bolster 20 laterally extends across the width of railcar 5 in substantial coexistence with shear plate 12, supporting the railcar and receiving the payload P from railcar side rails 10, located at the distal ends of car 5. From here, the loads are transferred into truck bolster 35. The car body bolster 20 has a medial center plate bowl 25 in mating relationship with center plate bowl 30 on bolster 35 for effectuating the transfer of the load. Load P then travels outwardly from bolster center plate bowl 30 towards bolster ends 33,37, where support springs 45 absorb the downward forces and transfer them into spring seats 50. Referring now to FIG. 1A, it is shown that spring seat 50 is integrally cast as part of sideframe 55, load P will be transferred throughout entire sideframe 55, including each of the pedestal jaws 60. Each of the pedestal jaws hold the axles 65 and wheels 70 which support the truck, meaning that load P will be transferred from wheels 70 into rail contact point 75.
It is important to understand that the sideframes described above are considered conventional truss-like sideframes, and regardless of whether they are fabricated or cast, a conventional truss sideframe consists of a separate, top member 55C and a bottom member 55T. FIG. 3 illustrates that when the bolster 35 (not shown) is vertically loaded, downwardly acting forces P are transferred into spring plate 50 and the axles counteract these forces at the sideframe ends 33,37, causing top member 55C to undergo compression and the lower member 55T to undergo tension or stretching. Since each member 55C, 55T is individually handling a specific type of load, (tension or compression), the sideframe structure is effectively behaving like a truss; hence the "truss" designation for the sideframe.
With the conventional loading scheme described above, a car body bolster 20 and a truck bolster 35 are both required for transferring loading forces from the car, into the trucks. Since the car body and truck bolsters are mated together, they will exhibit equal and opposite forces against each other. Unlike the sideframes, the car body and truck bolsters can be generally characterized as a simply supported beam having an intermediate load at its respective center plate area, and a beam bending moment in the region of the intermediate load will be present. In addition, a shear load will also be present and it is generally constant between the ends of the respective bolster and the intermediate load. Truck bolster shear and moment diagrams are provided in FIGS. 1c and 1d respectfully, and it should be understood that the car body bolster shear and moment diagrams are exactly the same in magnitude as the truck bolster shear and moment diagrams, but opposite in sign and direction. When a car body rolls relative to each of the truck sideframes, (See FIG. 2) the sidebearings 80 will take all or part of the truck bolster load, thereby shifting the shear and bending moment conditions to those depicted in FIGS. 2b and 2c, respectfully.
The conventional loading scheme described by FIG. 1 has one disadvantage; the load path between sideframe and spring seats and the truck bolster center plate 30, parallels the load path between the carbody center plate 25 and to the car body side rails 10. The redundancy of transferring the load P from the outside rails 10 of railcar 5 to the center of the body bolster 20, and then back outside again through the truck bolster 35 to springs 45 adds suspension components which are unnecessary. Eliminating unnecessary load paths and related components will result with substantial production and manufacturing cost savings, as well as fuel savings from pulling a lighter railcar. However, when eliminating major structural components such as a car or truck bolster, it should be understood that the remaining suspension components will experience loading and performance characteristics unlike a conventionally loaded railcar and truck. Therefore, there are many underlying performance factors to be considered with a suspension system even when minor structural modifications are made.
In U.S. Pat. No. 4,030,424, an early car body and truck suspension system was provided that utilized a less redundant loading path from the car body to the truck. Even though the car body utilized a car body bolster, the weight of the car was supported by bearing assemblies which were attached to the top surface of the bolster. This arrangement eliminated the need for a typical heavy car body bolster since the load was carried directly over the sideframes. However, it was discovered that this design had several notable operating disadvantages when compared to the present invention. Primarily, this system required the use of bulky, non-conventional sideframe members which were rigidly attached to both a lower transom member, and to a lightweight truck bolster. Even though the light truck bolster was said to allow torsional twisting, the rigidly connected transom and bolster forced the truck into maintaining a very rigid H-shaped configuration which had a tendency to crack under truck warping conditions. Truck warping is an out-of-square condition necessary for when the truck experiences movements other than simple relative sideframe-to-sideframe twisting. This means that when the sideframes experience longitudinal movement with respect to each other, the rigidly connected transom was incapable of providing the strength for curving, causing the truck to crack the transom at the sideframe connection. The transom arrangement, while rigidizing the truck, restricts the truck from being able to experience out-of-plane warping or other conditions caused by track irregularities. Another disadvantage of this particular design was that the truck bolster did not utilize the conventional friction shoe damping method for controlling truck bolster oscillations. Rather, the bolster was damped by a shock absorber which effectively tied the bolster to the sideframe. Furthermore, the bolster of the '424 patent had a bracketed connection attached to it which engaged the sideframe during undue vertical movement. Moreover, the bracket prevents longitudinal or twisting movements of the truck bolster when longitudinal out-of-plane conditions are experienced. However, since the sideframes were not constructed as a continuously solid truss-like structure, this truck required the use of a permanently attached and transversely disposed transom plate between the sideframes as a means for maintaining structural integrity, or else the truck would never have been able to withstand the operating forces.
Another disadvantage of the '424 design was found in the cumbersome sideframe members. These fabricated sideframes consisted of several interconnected members with the top plate member acting as the base for the spring set group; this is exactly opposite from a conventional truss sideframe where the bottom member is used to carry the spring group load. With the '424 truck, this means that the forces from the bearing assemblies are first transferred into the top plates of the sideframes before being transferred through several structural components before reaching the bottom sideframe plate. This sideframe arrangement has unnecessary structural components which also have to be structurally larger than those of a conventional truss sideframe.
The railcar and truck suspension system developed in U.S. Pat. No. 5,138,954, utilized a conventional truss sideframe while eliminating the car body bolster. This design utilized a laterally longer bolster which supported the car body at the railcar side rails, however, since the bolster carried the entire load P outwardly of each of the sideframes, it was discovered that this loading arrangement had several disadvantages. The main disadvantage found was that a longer-than-standard bolster was required to span beyond the sideframes. This meant that special molds and patterns had to be developed providing the bolster with only one specific application. Furthermore, in relation to the outward loading, the bolster also required an increased cross-sectional area for resisting larger bending moments present at the spring seats, when compared to a conventional bolster. This means that the bolster midsection has to be deeper and substantially heavier in mass than conventional trucks. In relation to a deeper midsection, a taller sideframe is also required in order to allow the bolster to vertically travel during its damping functions. This means that standard sized sideframes could not be used. A final shortfall of this design was that the longer bolster also required a very low coefficient of friction sliding means between it and the outboard car body support since the moment arm caused by the outwardly loaded bolster more significantly resisted turning and curving movements.